class Instrument:
    def make_sound(self):
        print("Instrument，发sheng")


class ErHu(Instrument):

    def make_sound(self):
        print("二胡发声")


class Piano(Instrument):
    def make_sound(self):
        print("钢琴发声")


class Violin(Instrument):
    def make_sound(self):
        print("小提琴发声")


def play(obj):
    obj.make_sound()


erhu = ErHu()
piano = Piano()
violin = Violin()
play(erhu)
play(piano)
play(violin)
